Elongate metal sections for use in the manufacture of window and door frame assemblies are commonly extruded from aluminum. As is well known, it is often desirable for the internal and external parts of the section to be thermally isolated from one another. (In this context "internal" means facing into the interior of the building in which the window or door is fitted, whereas "external" means facing the outside of the building and exposed to the elements.) This thermal isolation prevents the low temperature of the external parts being transmitted to the internal parts and resulting in undesirable condensation on the internal surfaces. To this end it is common practice to provide a thermal break by connecting the internal and external parts of the section only by means of a nonmetallic connector of low thermal conductivity.
There are two main methods currently used for providing such a thermal break. In a first method the section is formed from two separately preformed metal extrusions. These are connected together by preformed rigid non-metallic strips which are designed to interlock with the two metal extrusions respectively. Two non-metallic strips are often provided in spaced relation so as to form, with the metal extrusions, a hollow box section. There is then injected into this hollow box section a settable liquid plastics material, such as a plastics foam, the expansion and setting of which forces the non-metallic strips and metal extrusions into rigid fixed relation.
A second common method of manufacturing a section with a thermal break is by the method known as "pour and cut". According to this method the section is initially extruded in one piece and is so shaped as to define an upwardly facing open channel. The channel is then filled with a settable liquid of low thermal conductivity, usually a plastics resin, which is then allowed to set. The part of the section forming the bottom of the channel is then cut through longitudinally, usually by a circular saw. If necessary, any other parts of the section connecting the internal and external parts thereof are also sawn through so that the internal and external parts remain connected solely by the solidified resin, which thus provides the thermal break.
The latter method has certain advantages. In particular it may be less expensive than the first mentioned method since the apparatus required to perform the method is less costly and easier and cheaper to operate. However, disadvantages can arise in connection with the surface finish of the section. Such sections often need to be colored and various processes are known for providing the sections with a colored coating. There is no problem in using the "pour and cut" method when the section is to be a uniform color all over. However, it is sometimes desirable for the internal and external surfaces of the section to be of different colors, or otherwise of different surface finishes, and this may be difficult to achieve using the "pour and cut" method of forming a thermal break, since the surface finish must normally be applied to the section before the thermal break is formed and it is difficult to apply different colors to different parts of a single section. Sections formed by the "pour and cut" method, therefore, have hitherto normally been of the same color throughout, on both the internal and external surfaces.
The present invention sets out to provide a method whereby two different surface finishes may be achieved in a section where the thermal break is formed by the convenient and cheap "pour and cut" method.